15581 has 2 divisors, whose sum is σ = 15582.
Its totient is φ = 15580.
The previous prime is 15569. The next prime is 15583. The reversal of 15581 is 18551.
15581 is nontrivially palindromic in base 9.
It is a strong prime.
It can be written as a sum of positive squares in only one way, i.e., 12100 + 3481 = 110^2 + 59^2
It is a cyclic number.
It is not a de Polignac number, because 15581 - 210 = 14557 is a prime.
It is a super-2 number, since 2×155812 = 485535122, which contains 22 as substring.
Together with 15583, it forms a pair of twin primes.
It is a Chen prime.
It is a plaindrome in base 16.
It is a nialpdrome in base 5.
It is a congruent number.
It is not a weakly prime, because it can be changed into another prime (15583) by changing a digit.
It is a polite number, since it can be written as a sum of consecutive naturals, namely, 7790 + 7791.
It is an arithmetic number, because the mean of its divisors is an integer number (7791).
215581 is an apocalyptic number.
It is an amenable number.
15581 is a deficient number, since it is larger than the sum of its proper divisors (1).
15581 is an equidigital number, since it uses as much as digits as its factorization.
15581 is an evil number, because the sum of its binary digits is even.
The product of its digits is 200, while the sum is 20.
The square root of 15581 is about 124.8238759212.
The cubic root of 15581 is about 24.9765112714.
The spelling of 15581 in words is "fifteen thousand, five hundred eighty-one".